Spatial light modulator featured with an anti-reflective structure

ABSTRACT

A spatial light modulator supported on a device substrate includes a plurality of light modulation elements to modulate a light emitted from a light source. The spatial light modulator and the device substrate further comprises a cyclic structure on a surface of the spatial light modulator and/or the device substrate for preventing a reflection of the incident light from the cyclic structure. In an exemplary embodiment the cyclic structure includes cyclic structural elements having a distance between two cyclic elements shorter than the wavelength of an incident light for preventing a reflection of the incident light from the cyclic structure.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Non-provisional application of a ProvisionalApplication 60/830,171 filed on Jul. 12, 2006. The ProvisionalApplication 60/830,171 is a Continuation In Part (CIP) Application ofU.S. patent application Ser. No. 11/121,543 filed on May 4, 2005 now U.SPat. No. 7,268,932. The application Ser. No. 11/121,543 is aContinuation In Part (CIP) application of three previously filedApplications. These three applications are Ser. No. 10/698,620 filed onNov. 1, 2003, Ser. No. 10/699,140 filed on Nov. 1, 2003 now U.S. Pat.No. 6,862,127, and Ser. No. 10/699,143 filed on Nov. 1, 2003 now U.S.Pat. No. 6,903,860 by the Applicant of this patent applications. Thedisclosures made in these patent Applications are hereby incorporated byreference in this patent application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image display system. Moreparticularly, the present invention relates to an image displayapparatus with one or more spatial light modulators that includemicrostructures shorter than wavelength of an incident light forenhancing the contrast of an image.

2. Description of the Related Arts

Even though there are significant advances of the technologiesimplementing an electromechanical mirror device as a spatial lightmodulator (SLM) in recent years, there are still limitations anddifficulties when it is employed to provide a high quality image.Specifically, when the images are digitally controlled, the imagequality is adversely affected due to the fact that the images are notdisplayed with sufficient number of gray scales.

An electromechanical mirror device is drawing a considerable interest asa spatial light modulator (SLM). The electromechanical mirror deviceconsists of “a mirror array” arranging a large number of mirrorelements. In general, the mirror elements from 60,000 to severalmillions are arranged on a surface of a substrate in anelectromechanical mirror device. Referring to FIG. 1A, an image displaysystem 1 including a screen 2 is disclosed in a reference U.S. Pat. No.5,214,420. A light source 10 is used for generating light energy forilluminating the screen 2. The generated light 9 is further concentratedand directed toward a lens 12 by a mirror 11. Lenses 12, 13 and 14 forma beam columnator operative to columnate light 9 into a column of light8. A spatial light modulator (SLM) 15 is controlled on the basis of datainput by a computer 19 via a bus 18 and selectively redirects theportions of light from a path 7 toward an enlarger lens 5 and ontoscreen 2. The SLM 15 has a mirror array arranging switchable reflectiveelements 17, 27, 37, and 47 being consisted of a mirror 33 connected bya hinge 30 on a surface 16 of a substrate in the electromechanicalmirror device as shown in FIG. 1B. When the element 17 is in oneposition, a portion of the light from the path 7 is redirected along apath 6 to lens 5 where it is enlarged or spread along the path 4 toimpinge on the screen 2 so as to form an illuminated pixel 3. When theelement 17 is in another position, the light is not redirected towardscreen 2 and hence the pixel 3 is dark.

Each of mirror elements constituting a mirror device to function as aspatial light modulator (SLM) and each mirror element comprises a mirrorand electrodes. A voltage applied to the electrode(s) generates acoulomb force between the mirror and the electrode, thereby making itpossible to control and incline the mirror and the mirror is “deflected”according to a common term used in this specification for describing theoperational condition of a mirror element.

When a mirror is deflected with a voltage applied to the electrodes tocontrol mirror, the deflected mirror also changes the direction of thereflected light in reflecting an incident light. The direction of thereflected light is changed in accordance with the deflection angle ofthe mirror. The present specification refers to a state of the mirrorwhen a light of which almost the entirety of an incident light isreflected to a projection path designated for image display as an “ONlight”, while referring to a light reflected to a direction other thanthe designated projection path for image display as an “OFF light”.

And a state of the mirror that reflects a light of an incident light ina manner that the ratio of the light reflected to a projection path(i.e., the ON light) and that reflected so as to shift from theprojection path (i.e., the OFF light) is a specific ratio, that is, thelight reflected to the projection path with a smaller quantity of lightthan the state of the ON light is referred to as an “intermediatelight”.

According to a convention of present specification, it defines an angleof rotation along a clockwise (CW) direction as a positive (+) angle andthat of counterclockwise (CCW) direction as negative (−) angle. Adeflection angle is defined as zero degree (“0°”) when the mirror is inthe initial state, as a reference of mirror deflection angle.

Most of the conventional image display devices such as the devicesdisclosed in U.S. Pat. No. 5,214,420 implement a dual-state mirrorcontrol that controls the mirrors at a state of either ON or OFF. Thequality of an image display is limited due to the limited number of grayscales. Specifically, in a conventional control circuit that applies aPWM (Pulse Width Modulation), the quality of the image is limited by theLSB (least significant bit) or the least pulse width as control relatedto the ON or OFF state. Since the mirror is controlled to operate in aneither ON or OFF state, the conventional image display apparatuses haveno way to provide a pulse width to control the mirror that is shorterthan the control duration allowable according to the LSB. The leastquantity of light, which determines on the basis of the gray scale, isthe light reflected during the time duration according to the leastpulse width. The limited gray scale leads to a degradation of the image.

Specifically, FIG. 1C shows an exemplary control circuit for controllinga mirror element according to the disclosures made in U.S. Pat. No.5,285,407. The control circuit includes a memory cell 32. Varioustransistors are referred to as “M*” where “*” designates a transistornumber and each transistor is an insulated gate field effect transistor.Transistors M5 and M7 are p-channel transistors; while transistors M6,M8, and M9 are n-channel transistors. The capacitances C1 and C2represent the capacitive loads in the memory cell 32. The memory cell 32includes an access switch transistor M9 and a latch 32 a, which is basedof a Static Random Access Switch Memory (SRAM) design. The transistor M9connected to a Row-line receives a DATA signal via a Bit-line. Thememory cell 32 written data is accessed when the transistor M9 that hasreceived the ROW signal on a Word-line is turned on. The latch 32 aconsists of two cross-coupled inverters, i.e., M5/M6 and M7/M8, whichpermit two stable states, that is, a state 1 is Node A high and Node Blow, and a state 2 is Node A low and Node B high.

The mirror is driven by a voltage applied to the electrode abutting alanding electrode and is held at a predetermined deflection angle on thelanding electrode. An elastic “landing chip” is formed at a portion onthe landing electrode, which makes the landing electrode contact withmirror, and assists the operation for deflecting the mirror toward theopposite direction when a deflection of the mirror is switched. Thelanding chip is designed as having the same potential with the landingelectrode, so that a shorting is prevented when the landing electrode isin contact with the mirror.

Each mirror formed on a device substrate has a square or rectangularshape and each side has a length of 4 to 15 um. In this configuration, areflected light that is not controlled for purposefully applied forimage display is however inadvertently generated by reflections throughthe gap between adjacent mirrors. The contrast of image displaygenerated by adjacent mirrors is degraded due to the reflectionsgenerated not by the mirrors but by the gaps between the mirrors. As aresult, a quality of the image display is worsened. In order to overcomesuch problems, the mirrors are arranged on a semiconductor wafersubstrate with a layout to minimize the gaps between the mirrors. Onemirror device is generally designed to include an appropriate number ofmirror elements wherein each mirror element is manufactured as adeflectable micromirror on the substrate for displaying a pixel of animage. The appropriate number of elements for displaying image is incompliance with the display resolution standard according to a VESAStandard defined by Video Electronics Standards Association.Alternately, the number in compliance with the television broadcaststandards. In the case in which the mirror device has a plurality ofmirror elements corresponding to WXGA (resolution: 1280 by 768) definedby VESA, the pitch between the mirrors of the mirror device is 10 um andthe diagonal length of the mirror array is about 0.6 inches.

The control circuit as illustrated in FIG. 1C controls the micromirrorsto switch between two states and the control circuit drives the mirrorto oscillate to either an ON or OFF deflected angle (or position) asshown in FIG. 1A.

The minimum quantity of light controllable to reflect from each mirrorelement for image display, i.e., the resolution of gray scale of imagedisplay for a digitally controlled image display apparatus, isdetermined by the least length of time that the mirror controllable tohold at the ON position. The length of time that each mirror iscontrolled to hold at an ON position is in turn controlled by multiplebit words. FIG. 1D shows the “binary time periods” in the case ofcontrolling SLM by four-bit words. As shown in FIG. 1D, the time periodshave relative values of 1, 2, 4, and 8 that in turn determine therelative quantity of light of each of the four bits, where the “1” isleast significant bit (LSB) and the “8” is the most significant bit.According to the PWM control mechanism, the minimum quantity of lightthat determines the resolution of the gray scale is a brightnesscontrolled by using the “least significant bit” for holding the mirrorat an ON position during a shortest controllable length of time.

In a simple example with n bits word for controlling the gray scale, oneframe time is divided into (2^(n)−1) equal time slices. If one frametime is 16.7 msec, each time slice is 16.7/(2^(n)−1) msec.

Having set these time lengths for each pixel in each frame of the image,the quantity of light in a pixel which is quantified as 0 time slices isblack (no the quantity of light), 1 time slice is the quantity of lightrepresented by the LSB, and 15 time slices (in the case of n=4) is thequantity of light represented by the maximum brightness. Based onquantity of light being quantified, the time of mirror holding at the ONposition during one frame period is determined by each pixel. Thus, eachpixel with a quantified value which is more than 0 time slices isdisplayed by the mirror holding at an ON position with the number oftime slices corresponding to its quantity of light during one frameperiod. The viewer's eye integrates brightness of each pixel so that theimage is displayed as if the image were generated with analog levels oflight.

For controlling deflectable mirror devices, the PWM calls for the datato be formatted into “bit-planes”, where each bit-plane corresponds to abit weight of the quantity of light. Thus, when the brightness of eachpixel is represented by an n-bit value, each frame of data has then-bit-planes. Then, each bit-plane has a 0 or 1 value for each mirrorelement. In the PWM described in the preceding paragraphs, eachbit-plane is independently loaded and the mirror elements are controlledaccording to bit-plane values corresponding to them during one frame.For example, the bit-plane representing the LSB of each pixel isdisplayed as 1 time slice.

When adjacent image pixels are displayed with a very coarse gray scalescaused by great differences of quantity of light, thus, artifacts areshown between these adjacent image pixels. That leads to thedegradations of image qualities. The degradations of image qualities arespecially pronounced in bright areas of image when there are “biggergaps” of gray scale, i.e. quantity of light, between adjacent imagepixels. The artifacts are caused by a technical limitation that thedigitally controlled image does not obtain sufficient number of the grayscale, i.e. the levels of the quantity of light.

The mirrors are controlled either at ON or OFF position. Then, thequantity of light of a displayed image is determined by the length oftime each mirror holds, which is at the ON position. In order toincrease the number of the levels of the quantity of light, theswitching speed of the ON and OFF positions for the mirror must beincreased. Therefore the digital control signals need be increased intoa higher number of bits. However, when the switching speed of the mirrordeflection is increased, a stronger hinge for supporting the mirror isnecessary to sustain a required number of switches of the ON and OFFpositions for the mirror deflection. Furthermore, in order to drive themirrors provided strengthened hinge toward the ON or OFF positions,applying a higher voltage to the electrode is required. The highervoltage may exceed twenty volts and may even be as high as thirty volts.The mirrors produced by applying the CMOS technologies probably is notappropriate for operating the mirror at such a high range of voltages,and therefore the DMOS mirror devices may be required. In order toachieve a control of higher number of the gray scale, a more complicatedproduction process and larger device areas are required to produce theDMOS mirror. Conventional mirror controls are therefore faced with atechnical problem that the good accuracy of gray scales and range of theoperable voltage have to be sacrificed for the benefits of a smallerimage display apparatus.

There are many patents related to the control of quantity of light.These patents include U.S. Pat. Nos. 5,589,852, 6,232,963, 6,592,227,6,648,476, and 6,819,064. There are further patents and patentapplications related to different sorts of light sources. These patentsinclude U.S. Pat. Nos. 5,442,414, 6,036,318 and Application 20030147052.Also, The U.S. Pat. No. 6,746,123 has disclosed particular polarizedlight sources for preventing the loss of light. However, these patentsor patent applications do not provide an effective solution to attain asufficient number of the gray scale in the digitally controlled imagedisplay system.

Furthermore, there are many patents related to a spatial lightmodulation that includes the U.S. Pat. Nos. 2,025,143, 2,682,010,2,681,423, 4,087,810, 4,292,732, 4,405,209, 4,454,541, 4,592,628,4,767,192, 4,842,396, 4,907,862, 5,214,420, 5,287,096, 5,506,597, and5,489,952. However, these inventions do not provide a direct solutionfor a person skilled in the art to overcome the above-discussedlimitations and difficulties.

In view of the above problems, an invention has disclosed a method forcontrolling the deflection angle of the mirror to express higher grayscales of an image in a US Patent Application 20050190429. In thisdisclosure, the quantity of light obtained during the oscillation periodof the mirror is about 25% to 37% of the quantity of light obtainedduring the mirror is held on the ON position at all times.

According to such control, it is not particularly necessary to drive themirror at high speed. Also, it is possible to provide a higher number ofthe gray scale using a low elastic constant of the hinge that supportsthe mirror. Hence, such control makes it possible to reduce the voltageapplied to the landing electrode.

An image display apparatus using the mirror device described above isbroadly categorized into two types, i.e. a single-plate image displayapparatus equipped with only one spatial light modulator and amulti-plate image display apparatus equipped with a plurality of spatiallight modulators. In the single-plate image display apparatus, a colorimage is displayed by changing in turn the color, i.e. frequency orwavelength of projected light is changed by time. In a multi-plate theimage display apparatus, a color image displayed by allowing the spatiallight modulators corresponding to beams of light having differentcolors, i.e. frequencies or wavelengths of the light, to modulate thebeams of light; and combined with the modulated beams of light at alltimes.

In the single-plate image display apparatus and multi-plate imagedisplay apparatus, a configuration is such that the light illuminates awider zone than the array of spatial light modulators (SLMs). As aresult, it is possible to display a bright and uniform image across anentire image. Such a configuration, however, allows the reflection lightfrom parts illuminated by other than the arrayed light modulatorelements (e.g., mirrors) to incident to the projection lens. As aresult, the contrast of the image is degraded.

Also, the light arriving at a substrate from a gap between the adjacentlight modulation elements is reflected on the substrate to become anunnecessary reflection light. And the unnecessary reflection lightentering the projection path decreases the contrast of an image.

An improvement of the image is an important problem of an image displayapparatus, for which various contrivances are devised for spatial lightmodulators (SLMs) to solve the problem.

There is a method for layering a light absorption mask on a part otherthan the array of light modulator elements of a spatial light modulator(SLM) or forming a light absorption layer on light modulation elements.Such a configuration prevents an unnecessary reflection light fromentering the projection path.

As an example, in a mirror device arraying a plurality of deflectablemirror elements as light modulation elements, formed is ananti-reflection layer or light absorption layer on the surface otherthan the reflection surface of the mirror, such as the back thereof andthe top surface of the substrate retaining the mirror. Meanwhile, in aspatial light modulator (SLM) employing a liquid crystal as lightmodulation element, formed is an anti-reflection layer or lightabsorption layer in the components not contributing to an imagegeneration, such as a transistor and the wall surface between the liquidcrystal elements.

In order to make the anti-reflection layer as described above functioneffectively to an incident light possessing a wide wavelength band,however, a plurality of layers with different thick nesses must beformed. This consequently is faced with the problem of increasing thenumber of producing processes. On the other hand, a coating of a blackmaterial that is the simplest method for forming a light absorptionlayer is difficult to apply to a micro electro mechanical system (MEMS)device possessing a very minute structure. As an example, there is aproblem associated with the process for depositing a thin layer ofcarbon black in a specific place.

Note that there are following disclosure related to the problemdescribed above.

-   1. B. S. Thornton, “Limit of the moth's eye principle and other    impedance-matching corrugations for solar-absorber design”, JOURNAL    OF THE OPTICAL SOCIETY OF AMERICA VOLUME65, NUMBER3, MARCH 1975,    267-270.-   2. S. J. WILSON and M. C. HUTLEY, “The optical properties of ‘moth    eye’ antireflection surfaces”, OPTICA ACTA, 1982, Vol. 29, No. 7,    993-1009-   3. Eric B. Grann, M. G. Moharam, and A. Pommet, “Optimal design for    antireflective tapered two-dimensional sub wavelength grating    structures”, OPTICAL SOCIETY OF AMERICA Vol. 12, No. 2, February    1995, 333-339-   4. Philippe Lalanne and G Michael Morris, “Antireflection behavior    of silicon subwavelength periodic structures for visible light”,    Nanotechnology, 8, 1997, 53-56-   5. Yuzo Ono, Yasuo Kimura, Yoshinori Ohta, and Nobuo Nishida,    “Antireflection effect in ultrahigh spatial-frequency holographic    relief gratings”, APPLIED OPTICS, Vol. 26, No. 6, 15 Mar. 1987,    1142-1146 [Japan Patent Application] 2003-294910A, Sanyo Electric    Co., Ltd. [Japan Patent Application] 2001-27505, Japan Science and    Technology Agency

SUMMARY OF THE INVENTION

One aspect of the present invention is to provide a spatial lightmodulator (SLM) having a mirror surface formed with a cyclic structurewhich is shorter than a wavelength of an incident light for reducing areflecting light other than the modulating portion of a light reflectedfrom the SLM and a package for accommodating the spatial lightmodulator.

Another aspect of the present invention is to provide a spatial lightmodulator (SLM) or a package for a spatial light modulator (SLM) with ananti-reflective structure. Also, the present invention discloses animage display apparatus that implements the antireflective structureboth on the SLM and on the package to prevent unnecessary lightreflection such that the display quality is improved with bettercontrast because the interferences from the unnecessary reflecting lightis reduced.

Another aspect of the present invention is to provide a spatial lightmodulator that includes a device substrate for retaining a lightmodulation element modulating an incident light emitted from a lightsource, comprising a structural body having a cycle shorter than thewavelength of the incident light at least on either of a surface of thedevice substrate, of at least a part of the light modulation element orof at least a part of a package accommodating the device substrate.

Another aspect of the present invention is to provide an image displayapparatus comprising a spatial light modulator modulating an incidentlight emitted from a light source, comprising a structural body having acycle shorter than the wavelength of the incident light at least oneither of a surface of the device substrate, of at least a part of thelight modulation element constituting the spatial light modulator, of atleast a part of a package accommodating the spatial light modulator orsurfaces of optical members placed between the light source and aprojection lens.

Another aspect of the present invention is to provide a productionmethod of the spatial light modulator noted in the first aspect,featuring the structural body having a cycle shorter than the wavelengthof the incident light by either of imprinting method, etching method orsol-gel method.

The aspects of the present invention noted above make it possible toprevent a degradation of the contrast of an image caused by theunnecessary reflection light.

These and other aspects and advantages of the present invention will nodoubt become obvious to those of ordinary skill in the art after havingread the following detailed description of the preferred embodiment,which is illustrated in the various drawing figures

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a constitution of a conventional image display system witha spatial light modulator (SLM).

FIG. 1B shows a constitution and a control of a spatial light modulatoras shown FIG. 1A;

FIG. 1C shows an exemplary control circuit for a mirror element;

FIG. 1D shows the “binary time periods” in the case of controlling SLMby four bit words;

FIG. 2 is a diagonal view diagram of a spatial light modulator Arraying,on a device substrate, a plurality of mirror elements controlling areflection direction of an incident light by deflecting a mirror.

FIG. 3A is a cross-section diagram of a mirror element showing asituation of reflecting an incident light to a projection path bydeflecting a mirror;

FIG. 3B is a cross-section diagram of a mirror element showing asituation of not reflecting an incident light to a projection path bydeflecting a mirror;

FIG. 3C is a cross-section diagram of a mirror element showing asituation of reflecting an incident light to a projection path with anintermediate quantity of light by making a mirror oscillate freely;

FIG. 4 is an illustrative front cross-section diagram of an assemblybody accommodating a mirror device featuring with an anti-reflectionstructure by a package.

FIG. 5A is a front cross-section diagram of an assembly body featuredwith an anti-reflection structure on the inner wall of a packagesubstrate of a preferred embodiment 1;

FIG. 5B is a front cross-section diagram of an assembly body featuredwith an anti-reflection structure on the outer wall of a packagesubstrate of the embodiment 1;

FIG. 6 is a front cross-section diagram of an assembly body featuredwith an anti-reflection structure on the bottom surface of a mirror ofthe embodiment 1.

FIG. 7 is a front cross-section diagram of an assembly body featuredwith an anti-reflection structure on a cover member of the embodiment 1.

FIG. 8 shows an assembly body in which a transparent member such asglass constitutes a package accommodating a mirror device.

FIG. 9A is a plain view diagram of a mirror device featured with atwo-dimensional anti-reflection structure for a non-modulation mirrorelement;

FIG. 9B shows a configuration featured with a columnar anti-reflectionstructure, of which the tip is two-dimensional structure, on the bottomsurface of a mirror element.

FIG. 9C shows a configuration laying a layer featured with aone-dimensional anti-reflection structure on a light reflectionunnecessary unit, which has no purpose of reflecting light, of a covermember;

FIG. 9D shows a vertical cross-sectional diagram of adjacent ridgeshaving a cyclical triangular vertical section structure which isfeatured in one- and two-dimensional structures;

FIG. 10A shows an example of the producing process of a mirror devicehaving an anti-reflection structure;

FIG. 10B shows an example of the producing process of a mirror devicehaving an anti-reflection structure;

FIG. 11 is a configuration diagram of a single-plate image displayapparatus comprising a single spatial light modulator featured with ananti-reflection structure.

FIG. 12A is a front view diagram of a configuration of a two-plate imagedisplay apparatus comprising two of a spatial light modulator featuredwith an anti-reflection structure;

FIG. 12B is a rear view diagram of a configuration of a two-plate imagedisplay apparatus comprising two of a spatial light modulator featuredwith an anti-reflection structure;

FIG. 12C is a side view diagram of a configuration of a two-plate imagedisplay apparatus comprising two of a spatial light modulator featuredwith an anti-reflection structure;

FIG. 12D is a plain view diagram of a configuration of a two-plate imagedisplay apparatus comprising two of a spatial light modulator featuredwith an anti-reflection structure; and

FIG. 13 is a configuration diagram of a three-plate image displayapparatus comprising three of a spatial light modulator featured with ananti-reflection structure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to above briefly described drawings, the inventions includedin this patent application are illustrated by preferred embodiments of aspatial light modulator featured with an anti-reflection structure, of apackage accommodating the spatial light modulator, and of an imagedisplay apparatus that includes the aforementioned components. Exemplaryembodiments may include the spatial light modulator that is atransmissive liquid crystal device (LCD), a reflective liquid crystal ofsilicon (LCOS) or a mirror device. In the following descriptions, aspatial light modulator is used to exemplify the mirror devices,however, other types of mirror devices may also be applied to implementthe reflective structural features disclosed in the present invention.

FIG. 2 is a diagram of showing diagonal view of a spatial lightmodulator that includes a plurality of mirror elements disposed on adevice substrate as a mirror array for controlling a reflectiondirection of an incident light by controlling the deflecting angle of amirror. The mirror device 100 comprises a plurality of mirror elements101 disposed on a device substrate controlled by an electrode (not shownin a drawing herein) and supported on an elastic hinge (not shown in adrawing herein). A mirror 103 that is supported by an elastic hinge isshown in FIG. 2. Particularly in FIG. 2, mirror elements 101 are arrayedin a square matrix at regular intervals on the device substrate and eachmirror element includes a square mirror 103 and a dotted line representsthe deflecting axis for the mirror 103. The light emitted from a lightsource 102 in the vertical direction or diagonal direction in relationto the deflection axis 105 is incident to the mirror 103. Also, avoltage applied to an electrode supported on the device substrate 104controls the mirror 103 of one mirror element 101. The mirror pitchbetween adjacent mirrors 103 is preferably between 4 to 15 m. The“mirror pitch” refers to the distance between the deflection axes 105 ofthe adjacent mirrors 103. A “mirror gap” refers to the distance betweenedges of the adjacent mirrors 103. The shape of the mirror 103 or themirror gap and mirror pitch between the adjacent mirrors may be flexiblyadjusted to satisfy application specific requirements.

The operation of the deflection of the mirror 103 of the mirror element101 is described below by referring to the cross-sectional diagram of asingle mirror element 101 across the line. -I over the mirror device 100as shown in FIG. 2. FIG. 3A is the cross-section diagram of the mirrorelement 100 across the line I-I shown in FIG. 2. FIG. 3 illustrates themirror configuration of reflecting an incident light to a projectionpath by deflecting a mirror.

A control signal (0,1) is provided to a memory cell (not shown in adrawing herein) to apply a voltage of “0” volt to a electrode 108 a, andto apply a voltage Ve volts to a electrode 108 b, as illustrated in FIG.3A. As a result, the mirror 103 is deflected from a deflection angle of“0” degree to an angular position of +13 degrees toward the electrode108 b. The angular movement of the mirror is generated through a coulombforce when a voltage Ve volts is applied to the electrode 108 b. Thedeflected mirror 103 reflects the incident light to the projection path(i.e., an ON light state). It is noted that an insulation layer 106 isdeposited on the device substrate 104. A hinge electrode 109 iselectrically connected, and grounded, to the elastic hinge 107 throughan electric connection penetrating through the insulation layer 106.

FIG. 3B shows a cross-sectional view of the mirror element 100 acrossthe line I-I as that shown in FIG. 2 to illustrate the mirrorconfiguration when a deflecting mirror reflects an incident light awayfrom a projection path for image display.

A control signal (1,0) is provided to a memory cell (not shown in adrawing herein) to apply a voltage of Ve volts to a electrode 108 a, anda voltage of “0” volt is applied to a electrode 108 b as illustrated inFIG. 3B. As a result, the mirror 103 is deflected from a deflectionangle of “0” degree to an angular position of −13 degrees toward theelectrode 108 a. The angular movement of the mirror is generated througha coulomb force when the voltage of Ve volts is applied to the electrode108 a. The deflected mirror 103 reflects the incident light away fromthe projection path (i.e., an OFF light state).

FIG. 3C shows a cross-sectional view of the mirror element 101 acrossthe line I-I as that shown in FIG. 2 to illustrate the mirrorconfiguration when a deflecting mirror freely oscillates thuscontinuously repeating the ON-OFF cycles of the reflected light from theoscillating mirror projecting to and then away from the image projectionpath.

A control signal (0,0) is provided to a memory cell (not shown in adrawing herein) to apply “0” volt to both of the electrodes 108 a and108 b. The control signal (0,0) may be applied when the mirror 103 isdeflected in either of the states shown in FIG. 3A or 3B. As a result,the Coulomb force generated between the mirror 103 and the electrode isremoved thus allowing the mirror 103 to freely oscillate within therange of plus and minus 13 degrees in accordance with the characteristicof the elastic hinge 107. Depending on the free oscillation of themirror 103, the incident light is reflected to the projection path onlyin the range of a deflection angle in which the mirror becomes the ONstate. Therefore, the mirror 103 oscillates between the ON light stateand OFF light state continuously. A control of the number ofoscillations of the mirror 103 between the deflection angle of the ONlight state and that of the OFF light state makes it possible to adjustthe quantity of light reflected to the projection path.

In an exemplary embodiment, the deflection angle of the ON light stateof the mirror is the plus 13 degrees and that of the OFF light statethereof is the minus 13 degrees. The mirror freely oscillates betweenthe deflection angles of the ON light state and that of the OFF lightstate thus switches repeatedly between the ON light state and OFF lightstate. The control of the number of switches makes it possible to make aquantity of light of being less than that of the time of holding themirror completely at the ON state incident to the projection path. Forthis reason, it is possible to generate an intermediate quantity oflight between the ON light state and OFF light state. A control of thefree oscillation of the mirror enables a reduced controllable quantityof light to generate an image display with a higher number of grayscales than that of an image generated by using a conventional ON-OFFcontrol technique. Furthermore, there are additional flexibilities ofadjustment of the range of deflection of the mirror freely oscillatingfrom the present ±13° to different angular ranges such as ±8° and ±4°.

A mirror device that allows a free oscillation state further has thebenefits of a longer life of operation and operated at a lower voltagethan a conventional mirror device that operated only with two states,i.e., the ON light state and OFF light state. Furthermore, a highernumber of gray scales are achievable to provide image with improveddisplay quality.

Additional details related to the mirror element 101 are furtherdescribed below. The mirror 103 includes a mirror surface composed of ahigh reflectance metal such as aluminum, silver and gold. The mirror 103may have a multiple layer structure. The entirety or a part, e.g., abase part is attached to the device substrate 104. A neck part isattached to the mirror 103 with a middle part disposed between the baseand neck parts of the elastic hinge 107. The hinge 107 is composed of anelastic material to provide a force of restitution. The elastic hinge107 is made from aluminum, amorphous silicon, a single crystal siliconor such for example. The drive electrodes 108 a and 108 b are made froma conductor such as aluminum (Al), copper (Cu), tungsten (W), with acircuit connection configuration to allow for equal potentials on bothof the drive electrodes 108 a and 108 b. In an exemplary embodiment, themirror element includes an insulation layer 106 that is composed ofsilicone dioxide (SiO2) or silicon carbonate (SiC) and the hinge aresupported on a silicon substrate. It is understood that the materialcompositions and shapes for each part as described in the embodimentsmay be flexible changed to satisfy specific application requirements andmanufacturing processes.

An incident light projected to the “mirror array” with a configurationwherein a plurality of mirror elements are supported on the devicesubstrate 104 to reflect and modulate the incident light. Only themirror elements being a part of the mirror array may be allowed toreflect and modulate the incident light. Those mirror elements that areconfigured not to reflect or modulate the incident light are referred toas a “non-modulation mirror element”. The mirror device 100 as describedabove is contained and protected by a package from exposure to dust orphysical damages such that a device malfunction is prevented. Thepackage comprises a package substrate and a cover member. The mirrordevice is placed on the package substrate and covering the mirror devicewith the cover member joining with the package substrate particularlyconfigured to support and to protect the mirror device. The packagesubstrate is made of a metallic substrate, glass substrate or ceramicsubstrate.

In an exemplary embodiment, the cover member is made of glass. A part ofthe cover member includes a light-transmitting window to transmit anillumination light to project onto the mirror device.

Further details of an exemplary embodiment that includes an assemblybody of a mirror package provided with an anti-reflection structure aredescribed below.

Embodiment 1

A mirror device includes an anti-reflection structure is disclosed as apreferred embodiment 1. FIG. 4 illustrates an exemplary mirror devicethat includes an anti-reflection structure formed on the devicesubstrate. Specifically, FIG. 4 shows a front cross-section view of anassembly body 200 a that function as a package for accommodating amirror device. FIG. 4 shows only two mirror elements in the mirrordevice as an example. The assembly body 200 a comprises a mirror device,a package substrate 201 and a cover member 202. The package actuallyincludes other parts in additional to the mirror device. The packageincludes package substrate 201 and cover member 202 shown in FIG. 4 andthese parts are part of the package.

Further details for the constituent component of the assembly body 200 aare described below according what are shown in FIG. 4. It is understoodthat the term “inside of the package” noted in the present specificationrefers to a space sealing a mirror device. As an example, the spacesealed by the package substrate 201 and cover member 202 of FIG. 4 isreferred to as “inside of the package”. Referring to FIG. 4, the devicesubstrate 104 is placed on the package substrate 201, and the bottomsurface of the device substrate 104 and package substrate 201 are joinedtogether. And the mirror 103 supported by the elastic hinge 107 on thedevice substrate 104 has the role of reflecting and modulating theincident light emitted from the light source transmitted through thecover member 202. The top surface of the device substrate 104 isprovided with an anti-reflection structure. This anti-reflectionstructure on the top surface of the device substrate 104 prevents thedevice substrate from reflecting the incident light passing between themirror gaps. It is therefore possible to prevent an unnecessaryreflection of the incident light from the device substrate 104 to reducethe reflection light from entering the projection path. As a result, thecontrast of the displayed image is improved.

The package substrate 201 is joined to the cover member 202 forproviding an approximate sealed space for protecting the mirror devicefrom dust. The package substrate 201 may be composed of materials suchas glass substrate, silicon substrate, ceramic substrate or metallicsubstrate. As the package substrate 210 supports and protect the devicesubstrate 104 for the mirror device that includes plurality of mirrordevices. Furthermore, the package substrate supports and protects acontrol circuit for controlling a mirror device and a part of a flexibleprinted circuit board for controlling a mirror device. Note that thepackage substrate 201 may be made from the same material as that of thedevice substrate 104.

The cover member 202 is designed so as to cover over the mirror deviceand the cover member 202 is joined to the package substrate 201. Thecover member 202 has the major role of protecting the mirror 103 of themirror device from external dust. The cover member 202 may flexibly usedifferent glass materials or similar materials. As an example, silicaglass and PYREX glass (registered trademark of Corning, Inc.) areavailable. It is preferable to provide the distance between the topsurface of the mirror 103 and the bottom surface of the cover member202, which has at least 100 times of a mirror size. Such a configurationmakes it possible to widen an allowable range of coarseness of thesurface of the cover member 202. As an example, the surface of the covermember 202 is produced with the coarseness in the range of about 0.05 to0.15 μm/20 mm through 0.15 to 0.3/20 mm. The space in the inside of thepackage may be filled with gas or kept in an approximate vacuum. Joiningbetween the package substrate 201 and cover member 202 or between thepackage substrate 201 and device substrate 104 may be joined togetherwith a fritted glass or a joint layer composed of similar types ofmaterial compositions. The above descriptions are for the constituentcomponents of the assembly body 200 a according to the embodiment 1.

The next is a description of a design feature that an incident lightentering the assembly body 200 a is prevented from being reflected bythe anti-reflection structure particularly provided on the devicesubstrate 104 by referring to FIG. 4.

The incident light emitted from the light source enters the mirrordevice by way of the cover member 202. The incident light, which hasentered the mirror device, is reflected on the mirror 103. In thisevent, a part of the incident light passes through the mirror gapbetween the individual mirrors 103 and enters the device substrate 104.Meanwhile, the incident light reflected on the mirror 103 may further bereflected from the bottom surface of the adjacent mirror 103 and othersurround reflective surfaces, after entering the device substrate 104.These incident lights entering the device substrate 104 are preventedfrom being reflected by the anti-reflection structure now provided onthe device substrate 104. As such, the featuring of the anti-reflectionstructure makes it possible to suppress an unnecessary reflection of thelight arriving at the device substrate 104. This results in preventingan unnecessary reflection of light and the unnecessary reflection lightfrom entering the projection path, thereby enabling an improvement ofthe contrast of the image.

Embodiment 2

The following descriptions are for a package featured with ananti-reflection structure as an embodiment 2. The embodiment 2 is amodified example of the embodiment 1. The package according to theembodiment 2 is configured to feature an anti-reflection structure onthe internal and external wall surfaces of the package substrate of theembodiment 1. Other configuration of the embodiment 2 is similar to thatof the embodiment 1 and therefore the description is omitted here.

FIG. 5A is a front cross-section diagram of an assembly body 200 b-Ifeatured with an anti-reflection structure on the internal wall of thepackage substrate 201 of the embodiment 1. The assembly body 200 b-Ishown in FIG. 5A is featured with the anti-reflection structuredescribed above on the inner wall on the package substrate 201 b-I. Alight reflected on the mirror 103 is prevented from being furtherreflected on the inner wall of the package substrate 201 b-I by theanti-reflection structure featured on the inner wall of the packagesubstrate 201 b-I. As a result, the contrast of the image is improved.

FIG. 5B is a front cross-section diagram of an assembly body 200 b-Ifeatured with an anti-reflection structure on the outer wall of apackage substrate 201 of the embodiment 1. The assembly body 200 b-IIshown in FIG. 5B is featured with an anti-reflection structure on theouter wall of the package substrate 201 b-II. A reflection of anincident light at the time of entering the package substrate 201 b-II isprevented by the anti-reflection structure featured on the outer wall ofthe package substrate 201 b-II. This results in preventing thereflection light due to a reflection of the incident light on the outerwall of the package substrate 201 b-II from entering the projection pathand accordingly improving the contrast of the image.

The design feature of placing the anti-reflection structure on both ofthe device substrate 104 and package substrate 201 b-I, or on the devicesubstrate 104 and package substrate 201 b-II, as shown in FIGS. 5A and5B, makes it possible to further prevent a reflection of the incidentlight. Meanwhile, as shown in FIGS. 6, 7 and 9A described below, thebottom surface of the mirror 103 of the mirror element and/or the covermember 202 may also be featured with an anti-reflection structure. Notethat an anti-reflection structure may be featured on both of the innerand outer walls of the package substrate 201. Meanwhile, when a packagesubstrate 201 featured with an anti-reflection structure and thesubstrate is made of a light transmission member such as glass, aspecial advantage is achieved because the light transmits the packagesubstrate 201 while preventing a reflection of light at a part featuredwith the anti-reflection structure.

The anti-reflection structure of the present specification is of acyclic structure of no more than the wavelength of an incident light asdescribed later, and hence the structure has a tendency to be broken byan external force for instance. Therefore, it is preferable to configurethe anti-reflection structure for an inner wall of a package than anouter wall because of the fact the outer wall is vulnerable to anexternal force.

Embodiment 3

The next is a description on a mirror featured with an anti-reflectionstructure, as an embodiment 3. The embodiment 3 is a modified example ofthe embodiment 1. The embodiment 3 is configured to feature ananti-reflection structure on the bottom surface of the mirror 103 of theembodiment 1. Other configurations of the embodiment 3 are similar tothat of the embodiment 1 and therefore the description is omitted here.

FIG. 6 is a front cross-section diagram of an assembly body 200 cfeatured with an anti-reflection structure on the bottom surface of themirror 103 of the embodiment 1. The assembly body 200 c shown in FIG. 6is configured to feature an anti-reflection structure on the bottomsurface of the mirror 103. Such a configuration makes it possible toprevent a light reflected on the edge of the mirror 103 c from beingfurther reflected on the bottom surface of the adjacent mirror 103 c bythe anti-reflection structure featured on the bottom surface of theadjacent mirror 103 c. This results in preventing a reflection of thelight on the bottom surface of each mirror 103 c. A feature of formingan anti-reflection structure on both of the device substrate 104 andmirror 103 c as shown in FIG. 6 makes it possible to prevent further anunnecessary reflection of the incident light. It is further possible tofeature an anti-reflection structure on the package substrate 201 and/orcover member 202 as shown in FIGS. 5A and 5B described above and in FIG.7 described below.

Embodiment 4

The next is a description on a package featured with an anti-reflectionstructure as an embodiment 4. The embodiment 4 is a modified example ofthe embodiment 1. The embodiment 4 is configured to feature ananti-reflection structure on the cover member 202 according to theembodiment 1. Other configurations of the embodiment 4 are similar tothat of the embodiment 1 and therefore the description is omitted here.

FIG. 7 is a front cross-section diagram of an assembly body 200 dfeatured with an anti-reflection structure on a cover member 202 of theembodiment 1. The assembly body 200 d shown in FIG. 7 is configured tofeature the anti-reflection structure as described above on the covermember 202 d. Such a configuration prevents a reflection of an incidentlight on the cover member 202 d by the anti-reflection structure and theincident light enters the inside of the package. Also enabled is toprevent the light reflected by the mirror device from reflecting on thecover member 202 d, thereby preventing an unnecessary reflection lightcaused by the cover member 202 d from entering the projection path. As aresult, the contrast of the image is improved.

In the configuration shown in FIG. 7, the anti-reflection structure isformed on the top surface of the cover member 202 d; an anti-reflectionstructure, however, may be provided only on the bottom surface of thecover member 202 d. Furthermore, an anti-reflection structure may beformed on both of the top and bottom surfaces of the cover member 202 d.The feature of forming the anti-reflection structure on both of thedevice substrate 104 and cover member 202 d makes it possible to preventfurther an unnecessary reflection of the incident light. It is alsopossible to feature an anti-reflection structure on the packagesubstrate 201 of the package and/or the mirror 103 of the mirror elementas shown in FIGS. 5A, 5B and 6 described above.

As exemplified in the above embodiments 1 through 4, the anti-reflectionstructure can appropriately be implemented on the entirety, or a part,of the mirror device and/or package.

The next is a description of an effective example of featuring ananti-reflection structure on a package by referring to FIG. 8. FIG. 8shows an assembly body 200 e in which both of a package substrate 205and cover member 206 of a package accommodating a mirror device areconstituted by a transparent member such as glass. In the assembly body200 e, the mirror device is accommodated in a package constituted by atransparent package substrate 205 and a transparent cover member 206.Here, the transparent package substrate 205 and cover member 206 aremade from glass, but limited to it. Note that the mirror device is shownas a mirror array arraying a plurality of mirrors 103. And thetransparent package substrate 205 may be made of a flexible printedcircuit board, with a flexible cable 204 of the flexible printed circuitboard for controlling the mirror device extending from the inside tooutside of the package.

When the package includes a transparent member, a part of the incidentlight is reflected on the transparent member and enters the projectionpath, resulting in degeneration of the contrast of the image. This iswhy the entire surface of the package of the assembly body 200 e isfeatured with an anti-reflection structure (which is indicated bydiagonal lines). This configuration makes it possible to prevent areflection of the incident light on the transparent package substrate205 and cover member 206. This results in preventing an unnecessaryreflection light from entering the projection path, thereby enabling animprovement of the image. Note that, also in the case of using an LCD orLCOS as a spatial light modulator, a featuring of an anti-reflectionstructure on the wall of a device substrate retaining LC of LCD or LCOS;and/or a package of LCD or LCOS makes it possible to prevent anunnecessary reflection of light.

<Anti-Reflection Structure>

The description below provides details on an example of ananti-reflection structure by referring to FIGS. 9A, 9B, 9C and 9D. Theanti-reflection structure is a structure having a short cyclicstructure, which is shorter than the wavelength of a light, in onedirection on a plane and one having a short cyclic structure, which isshorter than the wavelength of a light, in two directions on a plane.The anti-reflection structure is a structure having a cyclic triangularvertical cross-sectional structure shorter than the wavelength of alight for example.

The present specification implements an antireflective structure thathas a cyclic triangular vertical cross-sectional structure, which isshorter than the wavelength of light, in one direction on a plane as“one-dimensional structure”. Meanwhile, the antireflective structure maybe implemented with a structure having a cyclic triangular verticalcross-sectional structure, which is shorter than the wavelength oflight, in two directions on a plane as “two-dimensional structure”. Theone-dimensional structure is, as an example, an accordion-shapestructure shown in FIG. 9C described later. The two-dimensionalstructure is, as an example, a structure of an approximate square coneor circular cone, that is, a cyclic triangular vertical cross-sectionalstructure of the two directions arranged in a matrix in a plane as shownin FIG. 9A described later.

The process of forming the anti-reflection structure may include aprocess of imprinting or to apply lithography methods in a MEMS processso that there is no need to deposit a light absorbing layer on a mirroras will hereinafter be described in detail. As a result, thesestructures have low reflectance for the wide wavelength bands and extendthe angular acceptance ranges. Also, problems such as a materialselection, an adhesion, a thermal endurance or a diffusion of the lightassociated with the conventional anti-reflection coating are eliminated.

The next is a description of an example of featuring an anti-reflectionstructure on a non-modulation mirror element by referring to FIG. 9A.

There is a particular mirror configuration of providing a larger numberof mirrors than the number of pixels satisfying a desired resolution ofan image in order to ease a position adjustment of a mirror device inrelation to a projection optical system of an image display apparatus orfor example to correct a trapezoidal distortion of the image. Anon-modulation mirror(s) not contributing to displaying the image mayexist depending on a setup of the image display apparatus. In such acase, the non-modulation mirror(s) is controlled in an always-OFF stateor such so as to prevent the light reflected on the non-modulationmirror(s) from entering the projection path. Even with such a control,some level of light still enters the projection path and a degradationof the contrast of the image is occurred. Therefore, a mirror(s)equivalent to the non-modulation mirror is featured with the aboveanti-reflection structure for improving a contrast of the image.

FIG. 9A is a plain view diagram of a mirror device featured with atwo-dimensional anti-reflection structure on a non-modulation mirrorelement. Note that the mirror element is shown by omitting componentsother than the mirror 103. And the non-modulation mirrors 103 areindicated by diagonal lines. The anti-reflection structure is featuredon the non-modulation mirrors 103 a in the exterior border region of themirror array that are not used as light modulating mirror elements asshown in FIG. 9A. A featuring of a cyclic square cone two-dimensionalstructure which is shorter than the wavelength of an incident light, forexample, on the non-modulation mirrors 103 a in the configuration ofFIG. 9A makes it possible to prevent a reflection of the light.

The description below provides details of an anti-reflection structurein the case when a light emitted from the light source is a polarizedlight by referring to FIGS. 9B and 9C. According to APPLIED OPTICS, Vol.32, Issue 14, pp 2582˜, 1993, “Analysis of anti reflection structuredsurfaces with continuous one-dimensional surface profiles” written byDaniel H. Raguin and G. Michael Morris, the polarization direction of anincident light and a cyclic anti-reflection structure show differenteffects depending on the relative direction of them. Therefore, theinvention disclosed in FIGS. 9B and 9C is to configure an incident lightand a cyclic anti-reflection structure to have a specific relativedirection, thereby making such a relative direction enables the mosteffective for improving the quality of image display. In a mirror deviceit is not required to emit a polarized light. However, in order toobtain a brighter image and a broad color gamut, a laser light sourcemay be a preferable light source for emitting a polarized light.

The following description is to describe a preferred condition of acyclic triangular vertical cross-sectional structure in one-dimensionaland two-dimensional structure of an anti-reflection structure byreferring to FIG. 9D. FIG. 9D shows the adjacent ridges of theantireflective structure configured with a cyclical triangular verticalcross-sectional structure. This structure is featured in one- andtwo-dimensional antireflective structures of an anti-reflectionstructure. FIG. 9D defines the distance between the apexes of adjacentridges 203 aa and 203 ab as “pitch”, the bottom side of one ridge 203 aaas “width” and the height from the bottom to top of one ridge as“height”. Taking these into consideration, a condition enabling aneffective reduction of the reflection of light has been identified. Thepreferable anti-reflection structure of the spatial light modulator(SLM) and/or the package are such that each ridge of cyclic triangularvertical cross-sectional structure is shorter than the wavelength ofincident light that satisfies a condition defined as:λ>P>λ/2, andH/W>3;where the P is the pitch between adjacent ridges of the cyclictriangular vertical cross-sectional structure, the λ is a wavelength ofthe incident light, the H is the height of a ridge of the cyclictriangular vertical cross-sectional structure, and the W is the basewidth of a ridge of the cyclic triangular vertical cross-sectionalstructure. Also, the length of the ridge of the cyclic triangularvertical cross-sectional structure may be appropriately determinedaccording to above optimal conditions.

The condition described above provides a good result in the wavelengthband of visible light, which is 440 nm to 720 nm. For example, thecyclic triangular vertical cross-sectional structure is featured by animprinting method used by a MEMS process described in a chapter for aproducing process below. Also, the cyclic triangular verticalcross-sectional structure is featured by a lithographic method used by aMEMS process described in the chapter for a producing process below. Theanti-reflection structure of each constituent component described inFIGS. 4 through 8 is, for instance, a one- or two-dimensional structurehaving the triangular vertical cross-sectional structure as describedabove. Note that the one-dimensional and two-dimensional structures maybe intermixed in one constitute component, e.g., a device substrate.

<Method for Featuring an Anti-reflection Structure on a Spatial LightModulator and on a Package>

The following description describes a method for featuring ananti-reflection structure on a spatial light modulator and on a package.The present embodiment is described on the method for featuring ananti-reflection structure on a mirror device by taking an example of aspatial light modulator. The processes of producing a mirror device withan anti reflection structure according to this embodiment is summarizedbelow.

FIGS. 10A and 10B show an example of the production process of a mirrordevice featuring an anti reflection structure according to the presentembodiment. In FIG. 10A, beginning from step 1, a drive circuit 303 anda wiring pattern 302 for driving and controlling the mirrors are formedin a semiconductor wafer substrate 301. In the step 2, the electrodes304 connected to the drive circuit 303 are formed on the wiring pattern302. Then, the drive circuit 303 formed in the semiconductor wafersubstrate 301 is tested to check for abnormality of the operation of thedrive circuit 303 and continuity of the electrodes 304. If noabnormality is detected in the drive circuit 303 and the electrodes 304in this step, the process proceeds to the next step. In the step 3, aninsulation layer 305 is formed on the electrodes 304. The insulationlayer 305 not only prevents an electrical short circuit during themirror operation but also prevents the electrodes from being erodedthrough etching in a subsequent step. Examples of the material of theinsulation layer 305 are SiC, Si3N4 and Si. Here, a constituent member,which is featured with the anti-reflection structure described abovehaving a shorter cycle than the wavelength of the incident light, e.g.,a visible light, is pressed on the insulation layer 305, therebytransfer-printing (noted as “transferred” hereinafter) the cyclicstructure of the anti-reflection structure to the insulation layer 305.Alternatively, the cyclic structure may be transferred to a layer, whichis a layer other than the insulation layer 305, e.g., a polyimide layerthat is an anti-reflection layer, provided additionally. The presentspecification calls such a method as an imprinting method.

Furthermore, the cyclic anti-reflection structure may be formed by usingan etching process that applies a lithographic technique, or othersimilar manufacturing processes. In such a case, the anti-reflectionstructure may be formed by combining an anisotropic etching with anisotropic etching, carrying out multiple times of etchings, or repeatingeither the anisotropic etching or isotropic etching processes. Thesemethods enable the formation of an anti-reflection structure on thedevice substrate of the mirror device.

In the step 4, a first sacrificial layer 306 is deposited on thesemiconductor wafer substrate 301 to form the drive circuit 303 andelectrodes 304 thereon. The first sacrificial layer 306 is used forforming mirror surfaces in a subsequent step, with a space providedbetween each of the mirror surfaces and semiconductor wafer substrate301. An example of the material of the first sacrificial layer 306 isSiO2. In this embodiment, thickness of the first sacrificial layer 306determines the height of an elastic hinge for supporting the mirror.

After the above process, a cyclic structure on the first sacrificiallayer 306 is formed by using the aforementioned imprinting method toprint the cyclic structure of the anti-reflection structure on thesurface of a structure body that will be deposited on a later processThe bottom surface of a mirror or that of a structure body is equivalentto the aforementioned component. The process forms the cyclicanti-reflection structure on the first sacrificial layer 306 by anetching process. In the step 5, etching is used for removing a part ofthe first sacrificial layer 306. The etching process is carried out inaccordance with a predetermined height and shape of the expected elasticmember as will be formed in a subsequent step. In the step 6, theelastic member 307 including a connection section connected to thesemiconductor wafer substrate 301 is deposited on the semiconductorwafer substrate 301 and the first sacrificial layer 306 is formed in thestep 4. In the present embodiment, the elastic member 307 will form theelastic hinge that supports the mirror later. Examples of the materialsof the elastic member 307 include silicon material such as singlecrystal silicon, poly-silicon, and amorphous silicon; and/or metals suchas aluminum and titanium and alloys of these metals. By adjusting theamount of deposition of the elastic member 307 in this step, the finalthickness of the elastic hinge is determined.

In the step 7, a photoresist 308 is deposited on the structure formed onthe semiconductor wafer substrate 301 in the previous steps. In the step8, a mask that transfers a desired structure shape is used to expose thephotoresist 308 and the elastic member 307 deposited on thesemiconductor wafer substrate 301 is then etched to form the desiredstructure shape. The etching in this step divides the elastic member 307deposited on the semiconductor wafer substrate 301 in the step 6 intoindividual elastic hinges corresponding to individual mirrors of mirrorelements in the mirror device. In the step 9, a second sacrificial layer309 is further deposited on the structure deposited on the semiconductorwafer substrate 301 in the step 8 and the preceding steps thereof. Thecomposition of the second sacrificial layer 309 may be the same as thatof the first sacrificial layer 306. For example, SiO2 is used. In thisstep, the second sacrificial layer 309 is deposited to be higher than atleast the upper surface of the elastic member 307.

In the step 10 shown in FIG. 10B, the photoresist 308 and secondsacrificial layer 309 deposited on the semiconductor wafer substrate 301in the step 9 and the preceding steps thereof are polished until theupper surface of the elastic member 307, which is the elastic hinge, isexposed. In the step 11, a mirror layer 311 is deposited in such a waythat it is connected to the upper surfaces of the photoresist 308 andelastic member 307 that have been exposed in the step 10. Examples ofthe material of the mirror layer 311 in this step include aluminum, goldand silver. Furthermore, in this step, in order to support the mirrorlayer 311 and strengthen the connection to the elastic hinge, or inorder to prevent in most cases a stopper from adhering to the mirrorwhen the mirror is deflected, a mirror support layer 310 made of amaterial different from that of the mirror may be formed between themirror layer 311 and elastic member 307. Examples of the materials ofthe mirror support layer 310 include titanium and tungsten. In the step12, a photoresist (not shown in a drawing) is coated on the mirror layer311 deposited in the step 11. After a mask is used to expose thephotoresist for forming a mirror pattern, the subsequent etchingprovides individually divided mirrors and shapes the mirrors. In thisstep (step 12), since the first sacrificial layer 306, photoresist 308and second sacrificial layer 309 are still present under the mirror; nodirect external force is applied to the elastic member 307. At the pointwhen such a structure is formed, it is possible to divide thesemiconductor wafer substrate 301 into individual mirror devices.However, a protective layer is desirably further formed on the mirrorlayer 311 preferably in the viewpoint of preventing a reduction inreflectance, for example, due to an attached foreign matter and ascratch on the mirror layer 311. By further depositing the protectivelayer on the mirror layer 311, it is possible to prevent contaminationof the elastic member 307 with foreign matter, destruction of theelastic member 307, attachment of foreign matter to the mirror andgeneration of scratches when dicing is used for dividing a plurality ofmirror layer 311 formed on the semiconductor wafer substrate 301 intoindividual mirror devices.

Then, the plural mirror layers 311 formed on the semiconductor wafersubstrate 301 are divided into individual mirror devices. The dicingstep for dividing the semiconductor wafer substrate 301 into individualmirror devices includes the sub-steps of attaching a UV tape that losesadhesion upon illumination of UV light to the backside of thesemiconductor wafer substrate 301, mounting the entire semiconductorwafer substrate 301 having the UV tape attached to the backside thereofto a frame of the dicing system, and using a circular blade that iscalled a diamond saw to cut the semiconductor wafer substrate 301. Afterthe semiconductor wafer substrate 301 is divided into individual mirrordevices, the UV tape is stretched to pull the cut mirror devices so asto create gaps between them. Therefore, the individual mirror devicesare completely separated from each other. Then, when a UV light isilluminated to the backside of the UV tape attached to the backsides ofthe completely-separated individual mirror devices, the adhesion is lostand hence the mirror devices are easily separated from the UV tape. Thedicing step is not limited to the diamond saw cutting described above,but may be performed by other methods, for example, a laser cutting, ahigh pressure water stream cutting, etching scribe lines using anotheretchant, and reducing the thickness of the semiconductor wafer substrate301 after scribe lines are formed.

After the step 12 is completed, in the subsequent step 13, the firstsacrifice layer 306, photoresist 308, second sacrifice layer 309 andprotective layer are removed by using an appropriate etchant, so thatthe mirrors protected by these layers become deflectable. In this way,the elastic members 307 and the mirror layers 311 can be formed on thesemiconductor wafer substrate 301 and deflected by using the drivecircuit 303 and electrodes 304. Finally, a completed mirror device isaccommodated in a package.

The anti-reflection structure of the mirror device can also be achievedby applying a sol-gel method for instance, in addition to the imprintmethod of transfer by the imprinting and the production method of achemical etching, e.g., the lithography. In the sol-gel method, forinstance, a coating of a solution of a mixture between an extremely fineparticle of a nanometer level and a sol or gel material on a targetbody, followed by drying the target body, makes it possible to feature afine structure on the target body. The use of the sol-gel method enablesthe forming of a fine structure on a plurality of members at once, andtherefore a large number of processes such as a conventional method forforming a plurality of anti-reflection layers are no longer required,resulting in improving productivity.

The method for providing an anti-reflection structure as described aboveis applicable to a package and other optical elements, e.g., a prism.Note that, also in the case of using an LCD or LCOS as a spatial lightmodulator, the use of the method described above enables a featuring ofan anti-reflection structure on the wall of a device substrate retainingLC (liquid crystal) of LCD or LCOS; or a package.

<Image Display Apparatus Comprising a Spatial Light Modulator, aPackage, and/or an Optical Element Featured with an Anti-reflectionStructure,>

The following description is related to an image display apparatuscomprising a spatial light modulator, a package, and/or an opticalelement featured with an anti-reflection structure, which is describedabove. The following drawing refers to a reflective spatial lightmodulator featured with an anti-reflection structure, e.g., a mirrordevice and a Liquid Crystal On Silicon (LCOS). Note that a use of atransmissive spatial light modulator, e.g., a Liquid Crystal Device(LCD), and an appropriate change of configuration of an image displayapparatus as described below make it possible to display an image, whichcan easily be understood by a person skilled in the art.

<Single-plate Image Display Apparatus>

To begin with, the following description is for an example of asingle-plate image display apparatus comprising a single spatial lightmodulator featured with an anti-reflection structure. FIG. 11 is aconfiguration diagram of a single-plate image display apparatus 400comprising a single spatial light modulator featured with ananti-reflection structure. The single-plate image display apparatus 400comprises the following constituent members. A light source 401 emits alight for projecting an image. A light source control unit 402 at aprocessor 410 controls the light source 401. The light source 401 may bean arc lamp or the like, or may be a laser light source or a lightemitting diode (LED). Or the light source 401 may be constituted by aplurality of sub-light sources. The light source control unit 402adjusts the number of the sub-light sources to turn on for controlling aquantity of light. The light source control unit 402 biases the positionof a sub-light source to turn on for controlling a locality of anintensity of light. For the light source 401 that includes a pluralityof laser light sources with different wavelengths, a changeover of eachlaser light source by means of the light source control unit 402 makesit possible to select a color of an incident light. Therefore, a colorwheel 406 described later is not required. Also possible is a pulseemission of light of a laser light source or light emitting diodesource.

When using a near-parallel flux of light with a small light dispersionangle such as a laser light source, the numerical aperture NA of anillumination light flux reflected on the mirror device that is a spatiallight modulator can be reduced based on the relation of etendue. Bythis, while avoiding an interference of the illumination light fluxprior to being reflected on the mirror device with the projection lightflux after being reflected thereon, these fluxes can be moved close toeach other. As a result, the mirror can be downsized and also the mirrorcan be implemented with a smaller deflection angle. With a smallermirror deflection angle it is feasible to more the illumination lightflux and projection light flux closer to each other to shorten thedifference of light path lengths between the incident light andreflection light passing through the package and make the difference oftransmission of the package smaller. Larger amount of incident light orreflection light enter the mirror array or projection path. Therefore,making the deflection angle of the mirror small by using a laser lightsource enables a provision of brighter image. A condenser lens-1 403focuses the light from the light source. A rod integrator 404 uniformsan intensity of light. A condenser lens-2 405 focuses the light outputfrom the rod integrator 404. A color wheel 406 includes a filter membercomprising a plurality of filters. Each of the individual filtersextracts a specific wavelength. As an example, the filter member mayinclude three filters, e.g., a filter for extracting the light of thewavelength of red, one for extracting the light of the wavelength ofgreen and one for extracting the light of the wavelength of blue. And,each filter of a light-passing path can be changed over by rotating orsliding the filter member constituted by the filters by a color wheeldrive unit 407. The filter may have a deflection characteristic. A motorcontrol unit of the processor 410 controls the color wheel drive unit407. The color wheel drive unit 407 controls the rotation or slide speedof the filter. A total internal reflection (TIR) prism 409 includes twotriangle prisms, i.e., a first prism 411 and a second prism 412. Thefirst prism 411 has the role of totally reflecting the incident light.As an example, the first prism 411 totally reflects the incident lightto the light path entering the reflective spatial light modulator. Thetotally reflected light is modulated by the reflective spatial lightmodulator and reflected to the second prism 412. The second prism 412transmits the reflection light incident thereto below a critical angle.The respective surfaces of the first prism 411 and second prism 412 mayfurther comprise an anti-reflection structure.

FIG. 11 shows a package containing a spatial light modulator 414. Thespatial light modulator 414 shown in FIG. 11 is a mirror device or LCOSthat is a reflective spatial light modulator featured with theanti-reflection structure as described above. An anti-reflectionstructure may also be formed on the package 413 as described above. AnSLM control unit 415 of the processor 410 controls the spatial lightmodulator 414. A projection lens 416 has the function of enlarging thelight reflected and modulated by the spatial light modulator 414 so asto project the light on a screen 417. The processor 410, comprising alight source control unit 402, a motor control unit 408 and a spatiallight modulator control unit 415, is capable of synchronouslycontrolling each of the aforementioned control units by combining them.The processor 410 is connected to an image signal input unit 418 toreceive and process image signal data. The processor 410 is furtherconnected to the frame memory 419 for sending the processed image signaldata. The image signal input unit 418 inputs the incoming image signaldata to the processor 410. The frame memory 419 is capable of storingthe image signal data of a single image processed by the processor 410.These are the constituent members comprised by the single-plate imagedisplay apparatus 400 shown in FIG. 11.

The following description describes the principle of displaying a colorimage at the single-plate image display apparatus 400 shown in FIG. 11.In the single-plate image display apparatus 400, the light emitted fromthe light source 401 enters a filter of the color wheel 406 by way ofthe condenser lens-1 403, rod integrator 404 and condenser lens 405. Thelight extracted only the light of a specific wavelength by a filter ofthe color wheel 406 enters the first prism 411 of the TIR prism 409. Andthe light reflected by the first prism 411 of the TIR prism 409 entersthe spatial light modulator 414 accommodated in the package 413. In thisevent, a reflection of the incident light by the cover member of thepackage 413 and by the device substrate of the spatial light modulator414 can be reduced because both the package 413 and spatial lightmodulator 414 are featured with the anti-reflection structure asdescribed above.

The light reflected and modulated by the mirror element of the spatiallight modulator 414 re-enters the TIR prism 409 and transmits the secondprism 412 thereof. Then the transmitted light is projected on the screen417 by way of the projection lens 416. When displaying an image as such,the light source control unit 402 in the processor 410 controls thequantity of light or such, emitted from the light source based on theimage signal data incoming by way of the image signal input unit 418.The motor control unit 408 is controlled based on the image signal data,and the motor control unit 408 controls the color wheel drive unit 407.And, the control for changing over filters of the color wheel 406 isperformed by the color wheel drive unit 407. Furthermore, the SLMcontrol unit 415 controls the plurality of light modulation elements ofthe spatial light modulator 414 based on the image signal data. Thesingle-plate image display apparatus 400 configured as described abovedivides a period for displaying one image (i.e., one frame) intosub-frames corresponding to the individual wavelengths of light inrelation to the respective wavelengths of light, e.g., a wavelengthcorresponding to red, one corresponding to green and one correspondingto blue. And the light of each wavelength is illuminated to the spatiallight modulator 414 in accordance with a period of each sub-frame.According to such image display time sequence, the period of eachsub-frame, the period of modulating the light of each wavelength at thespatial light modulator 414 and the period of stopping a filter of thecolor wheel 406 are mutually dependent. A selective reflection of theincident light at the spatial light modulator 414 enables only the lightof the individual wavelength reflected to the projection path to beprojected to the screen. And a sequential projection of lights of theindividual wavelengths in accordance with the respective sub-frameperiods enables a display of a color image.

The following description describes an example of a multi-plate imagedisplay apparatus comprising a plurality of spatial light modulatorsfeatured with an anti-reflection structure. The multi-plate imagedisplay apparatus comprises a plurality of light sources, a plurality ofspatial light modulators and a projection lens. The light source maypreferably be a laser light source or a light emitting diode (LED). Aplurality of laser light sources may be equipped, with each light sourcebeing independently controlled. The independent control of each lightsource can eliminate a color filter by turning off a laser light sourcehaving a prescribed wavelength. The use of a laser light source enablesa pulse emission that has been difficult to achieve with a mercury lamp.Note that a plurality of spatial light modulators are respectivelyreferred to as reflective spatial light modulators likewise thesingle-plate spatial light modulator described above.

The following description describes the configuration and principle todisplay an image of a two-plate image display apparatus and three-plateimage display apparatus as an example of multi-plate image displayapparatus comprising a package and a plurality of spatial lightmodulators featured with an anti-reflection structure.

<Two-plate Image Display Apparatus>

The two-plate image display apparatus is configured to make two spatiallight modulators corresponding respectively to two groups of lightsources. And one spatial light modulator modulates the light emittedfrom one group of light sources and another spatial light modulatormodulates the light emitted from another group of light sources. Then,the reflected and modulated light by each of the spatial lightmodulators is synthesized, thereby displaying an image. As an example,when displaying an image with the lights of wavelengths corresponding tothree colors, i.e., red light, green light and blue light, green lighthaving the high luminosity factor is modulated by one spatial lightmodulator, and red and blue lights are modulated by another spatiallight modulator in sequence or simultaneously, followed by synthesizingthe light modulated by each spatial light modulator and displaying animage.

FIGS. 12A through 12D are configuration diagrams of a two-plate imagedisplay apparatus comprising two of a spatial light modulator featuredwith an anti-reflection structure accommodated in one package. The imagedisplay apparatus 500 shown in FIGS. 12A through 12D comprises a greenlaser light source 501, red laser light source 502, blue laser lightsource 503, illumination optical systems 504 a and 504 b, two triangleprisms 506 and 508, two spatial light modulators 520 and 530 which areaccommodated in one package 511, a circuit board 508, a joint member512, a light shield member 513, a light guide prism 514 and a projectionoptical system 523.

The following description describes the constituent components of theimage display apparatus 500 shown in FIGS. 12A through 12D. Theindividual light sources 501, 502 and 503 are laser light sources asdescribed for the single-plate image display apparatus and capable ofperforming a pulse emission. They may be comprised of a plurality ofsub-laser light sources alternatively. The light source may use twomercury lamps corresponding to the respective spatial light modulators.In the case of using the mercury lamps, an equipment of a filter 505allowing a passage of only a light of a specific wavelength whilereflecting other light of wavelengths on the surface of synthesizing thereflection light in a prism 510 described later provides a similareffect as a color filter. Alternatively, using a dichroic prism ordichroic mirror, thereby illuminating the spatial light modulator withthe light of the separated wavelength, may separate a wavelength oflight. The illumination optical systems 504 a and 504 b are opticalelements such as collector lenses described for the single-plate imagedisplay apparatus, rod integrators, convex lenses or concave lenses.

The prism 510 by combining two triangle prisms 506 and 509 has the roleof synthesizing the reflection lights from the two spatial lightmodulators 520 and 530. When the prism 510 synthesizes the reflectionlights from the individual spatial light modulators, it may beappropriate to equip the filter 505, e.g. a dichroic filter, allowing apassage of only a light of a specific wavelength while reflecting otherlight of wavelengths on the surface of synthesizing the reflection lightin a prism 510. Note that an anti-reflection structure can be featuredon the surface of the prism 510. The filter 505 has the same role as acolor filter because of a capability of allowing a passage of only alight of a specific wavelength while reflecting other light ofwavelengths. Meanwhile, when using a laser light source emitting a lighthaving a specific deflection direction, a deflection light beam splitterfilm separating/synthesizing light by using a difference of deflectiondirection of light on the surface of synthesizing a reflection light inthe prism 510 may be used, or a deflection light beam splitter coatingmay be applied to the aforementioned surface.

The package 511 is similar to the package provided with theanti-reflection structure described for the single-plate image displayapparatus. The package 511 noted in FIGS. 12A through 12D is configuredto be capable of accommodating two spatial light modulators 520 and 530within one package 511. The spatial light modulators 520 and 530 may beaccommodated in separate packages, however. The spatial light modulators520 and 530 are similar to the spatial light modulator featured with theanti-reflection structure described for the single-plate image displayapparatus. Note that FIGS. 12A through 12D show the mirror arrays 521and 531, and device substrates 533 and 532, of the respective spatiallight modulators 520 and 530. The circuit board 508 is connected to aprocessor, which is similar to the processor implemented for thesingle-plate image display apparatus described above. The processorcomprises a spatial light modulator control unit and a light sourcecontrol unit. And the processor processes the input image signal dataand reports the processed information to the spatial light modulatorcontrol unit and light source control unit. The spatial light modulatorcontrol unit and light source control unit control the spatial lightmodulator and light source respectively by way of the circuit board 508based on the processed information. The control of the spatial lightmodulator can be synchronized with that of the light source. The inputof the image signal data to the processor and other activity have beendescribed for the single-plate image display apparatus and thereforeomitted here.

The joint member 512 has the role of joining the prism 510 to thepackage 511. A material used for the joint member 512 includes a frittedglass for example. The light shield member 513 has the role of shieldingunnecessary light. A material used for the light shield member 513includes graphite for example. The image display apparatus 500 shown inFIGS. 12A through 12D is equipped with the light shield member 513 notonly on a part of the bottom of the prism 510 but also on the back ofthe prism 510. The light guide prism 514 is a prism by adhesivelyattaching the slope face on the front face of the prism 510 with thebottom of the light guide prism 514 facing upward. And the light guideprism 514 is equipped so that the individual light sources 501, 502 and503, the illumination optical systems 504 a and 504 b corresponding tothe respective light sources and the light axis of the light emittedfrom the individual light sources 501, 502 and 503 are respectivelyperpendicular to the bottom of the light guide prism 514. Thisconfiguration enables the lights emitted from the individual lightsources 501, 502 and 503 to be perpendicular to incident to the lightguide prism 514 and prism 510. This results in enabling a minimum of thereflection of lights occurred by the light guide prism 514 and prism 510when the lights emitted from the individual light sources 501, 502 and503 enters the light guide prism 514 and prism 510. Note that ananti-reflection structure can be provided on the surface of the lightguide prism 514.

The projection optical system 523 is an optical element for displayingan appropriate image to the screen. As an example, the projection systemmay include a projection lens for enlarging the light for displaying animage to the screen. Note that, when using both of a light sourceemitting a polarized light and a polarization beam splitter film, atwo-plate image display apparatus can be configured by using a ½wavelength plate or ¼ wavelength plate on the surface of the prism 501.FIGS. 12A to 12D show the two plate image display apparatus 500 with theconstituent members.

The following description describes the principle to display an image ofthe two-plate image display apparatus 500 by referring to FIGS. 12Athrough 12D. In the image display apparatus 500, the green laser light515, red laser light 516 and blue laser light 517 are entered to thefront direction of the prism 510. The individual laser lights 515, 516and 517 are reflected back to the prism 510 by two spatial lightmodulators 520 and 530 provide with the anti-reflection structure asdescribed above. Then, the respective laser lights 515, 516 and 517reflected on the backside of the prism 510 are synthesized and thecombined image is projected to the screen by the projection opticalsystem 523.

FIG. 12A is a front view diagram of a two-plate image display apparatuscomprising two spatial light modulators featured with an anti-reflectionstructure.

The following description describes the principle of the image displaybetween the incidence of the individual laser lights 515, 516 and 517from the front direction of the prism 510 and the reflection of therespective laser lights 515, 516 and 517 back to the prism 510 by twospatial light modulators 520 and 530. The green laser light source 501,red laser light source 502 and blue laser light source 503 projectindividual laser lights 515, 516 and 517 respectively through theillumination optical systems 504 a and 504 b corresponding to theindividual laser lights 515, 516 and 517, and enters the prism 510 byway of the light guide prism 514. Then the green laser light 515 and thered and blue laser lights 516 and 517 transmit into the prism 510, andenter into the package, which is featured with the anti-reflectionstructure that is joined to the bottom of the prism 510. With theanti-reflection structure formed on the surface of the light guide prism514 and prism 510, the reflections of the individual laser lights on therespective incident surfaces of prisms from the individual laser lights515, 516 and 517 projected through these surfaces, can be suppressed.The unnecessary light entering the projection path can accordingly bereduced. This results in improving the contrast of the image. Afterpassing through the package 511 provided with the anti-reflectionstructure, the green laser light 515 and the red and blue laser lights516 and 517 enter the two spatial light modulators 520 and 530 containedin a single package 511 and configured to receive and modulateindividual laser lights 515, 516 and 517. The modulated laser lightsfrom the respective spatial light modulators 520 and 530, the laserlights 515, 516 and 517 are reflected back to the prism 510.

The following description describes the principle of the image displayfrom the reflection of the individual laser lights 515, 516 and 517 atthe respective spatial light modulators 520 and 530 to display an imageby referring to the rear view diagram of the two-plate image displayapparatus 500 shown in FIG. 12B. FIG. 12B is a rear view diagram of aconfiguration of a two-plate image display apparatus comprising two of aspatial light modulator featured with an anti-reflection structure. Agreen laser ON light 518 and a red and blue laser-mixed ON light 519reflected to the back direction of the prism 510 from the respectivespatial light modulators 520 and 530 in the ON state are re-transmittedthrough the package 511, thus entering the prism 510. Then, the greenlaser ON light 518 and the red and blue laser-mixed ON light 519 arereflected on the outer surface of the prism 510 respectively. Then thegreen laser ON light 518 is re-reflected from the film 505 allowing apassage of only a light of a specific wavelength while reflecting thelight of other wavelengths. Meanwhile, the red and blue laser-mixed ONlight 519 is transmitted through the film 505. Then, the green laser ONlight 518 and the red and blue laser-mixed ON light 519 are synthesizedon the same optical path and incident together to the projection opticalsystem 523, thereby displaying a color image. The optical axes of therespective ON lights 518 and 519 entering the projection optical system523 from the prism 510 are preferably perpendicular to the surface ofthe prism 510. Such a configuration makes it possible to minimize areflection of light on the surface of the prism 510. This results inreducing a loss of the quantity of light of the respective ON lights 518and 519. Therefore, the configuration as described above enables adisplay of image at the two-plate image display apparatus 500 thatincludes two of the spatial light modulator and provided with theanti-reflection structure.

FIG. 12C is a side view diagram of a configuration of a two-plate imagedisplay apparatus that includes two spatial light modulators providedwith an anti-reflection structure. The green laser light source 501projects the green laser light 515 through the illumination opticalsystem 504 a perpendicular to the light guide prism 514. With the greenlight projected perpendicular into the optical guide prism 514 thusreduces a reflection of the green laser light 515. As a result, a lossof the green laser light 515 is minimized. After transmitting throughthe light guide prism 514, the green laser light 515 transmits throughthe prism 510 that is joined with the light guide prism 514 and entersinto the mirror array 521 of the spatial light modulator 520accommodated in the package 511. The mirror array 521 reflects theincident green laser light 515. When the deflection angle of the mirroris controlled at the ON state the entire reflection light enters theprojection optical system 523. When the deflection angle of the mirroris controlled at the intermediate light state, a portion of thereflection light enters the projection optical system 523. When thedeflection angle of the mirror is controlled at the OFF light state, thereflection light is reflected away and none of the reflection lightenters the projection optical system 523. A green laser light 524 isreflected on the mirror array 521 controlled at the ON light state, andthus the entire light enters the projection optical system 523.Meanwhile, a laser light 525 is reflected on the mirror array 521controlled at the intermediate state, and thus a portion of the lightenters the projection optical system 523. And a laser light 526 isreflected by the mirror array 521 controlled at the OFF light state toproject toward the light shield layer 513 provided on the back surfaceof the prism 510. And the reflected laser light 526 is absorbed in lightshield layer 513. By this, the green laser lights by the ON light in themaximum light quantity, by the intermediate light in the intermediatelight quantity between the ON light and OFF light, or by the OFF lightin the zero light quantity are incident to the projection optical system523.

By controlling and holding the deflection angle of the mirror betweenthe ON light state and OFF light state makes it possible to create anintermediate state. By controlling the mirror to operate at a freeoscillation state as described above enables the mirror to deflectrepeatedly to different angles including the deflection angles of anON-state, an intermediate state and an OFF-state. By controlling thenumber of free oscillations within a specific time duration makes itpossible to adjust a quantity of light incident to the projectionoptical system 523. The controllable amount of light projected during anintermediate state provides additional controllable gray scales todisplay the image at a higher level of gray scale resolutions. The sametechniques can be applies on the reverse surface for process andmanaging the gray scales of red light image display with a red lasersource 502 and also the blue laser light source 503.

FIG. 12D is a functional diagram for illustrating a configuration of atwo-plate image display apparatus comprising two of a spatial lightmodulator featured with an anti-reflection structure. The light ofprojected from a mirror controlled at an OFF light state is absorbed bythe light shield layer 513 on the back. No reflection light is projectedon the slope surface of the prism 510 when the individual spatial lightmodulators 520 and 530 are placed at 45 degrees in relation to the foursides of the outer circumference of the package 511 on the samehorizontal plane as shown in FIG. 12.

<Three-plate Image Display Apparatus>

The following description describes a three-plate image displayapparatus. The three-plate image display apparatus includes threespatial light modulators correspondent to three respective lightsprojected from three groups of light sources. The individual spatiallight modulators is arranged to modulate the individual lights emittedfrom the respective light sources. Then the image display systemsynthesizes the individual lights modulated by the respective spatiallight modulators for displaying an image. As an example, when displayingan image by the lights of three colors, i.e., red light, green light andblue light, the individual lights are continuously modulated by therespective spatial light modulators and the modulated individual lightsare synthesized, thereby displaying a color image.

FIG. 13 is a diagram for illustrating the configuration of a three-plateimage display apparatus comprising three spatial light modulatorsprovided with an anti-reflection structure. The image display apparatus600 shown in FIG. 13 comprises a light source 601, a condenser lens-1602, a rod integrator 603, a condenser lens-2 604, a condenser lens-3605, a TIR prism 608, a first dichroic prism 609, a second dichroicprism 610, a third prism 611, individual spatial light modulators 612,613 and 614, and individual packages 615, 616 and 617 accommodating theindividual spatial light modulators 612, 613 and 614 and a projectionlens 618.

The following description describes the constituent members of the imagedisplay apparatus 600. The light source 601 may be a mercury lampsource, a laser light source, an LED, or may also include the lightsource described for the single plate image display apparatus andtwo-plate image display apparatus as described above. The configurationand operation, such as the sub-light source and pulse emission, aresimilar to the light source for the image display apparatus describedabove and therefore the description is omitted here. The condenserlens-1 602, rod integrator 603, condenser lens-2 604 and condenserlens-3 605 are similar to those described for the single plate imagedisplay apparatus and the condenser lens-1 602, condenser lens-2 604 andcondenser lens-3 605 have the role of focusing the light. Meanwhile, therod integrator 603 has the function of projecting a light with a uniformintensity. The TIR prism 608 is similar to the prism described for thesingle-plate image display apparatus described above and therefore thedescription is omitted here. Note that the TIR prism 608 used for thethree-plate image display apparatus shown in FIG. 13 includes a firstprism 606 and a second prism 607. The first dichroic prism 609 andsecond dichroic prism 610 are prisms transmitting only the light of aspecific wavelength while reflecting the light of other wavelengths. Andthe third prism 611 is a regular prism. Note that the first dichroicprism 609 and second dichroic prism 610 may also implemented withdichroic mirrors.

FIG. 13 shows an image display system implemented with first dichroicprism 609 reflecting only a light of the wavelength equivalent to redwhile transmitting a light of other wavelengths to pass through and thesecond dichroic prism 610 reflecting only a light of the wavelengthequivalent to blue while transmitting a light of wavelengths other thanthe red light to pass through. The third prism 611 carries out a samefunction for a light of the wavelength equivalent to green light projectalong a straightforward direction. The surface of the individual prisms609, 610 and 611 are formed with the anti-reflection structure describedabove. Each of the packages 615, 616 and 617 is featured with theanti-reflection structure described above. The individual packages 615,616 and 617 accommodate the respective spatial light modulators 612, 613and 614. Each of the spatial light modulators 612, 613 and 614 is areflective spatial light modulator featured with the anti-reflectionstructure describe above. In an exemplary embodiment, the mirror deviceis implemented as a LCOS device. The projection lens 618 performs thefunction of enlarging individual lights synthesized after the individuallights are reflected and modulated at the respective spatial lightmodulators 612, 613 and 614. A processor 620 is basically similar to theone described for the single plate image display apparatus, andcomprises a spatial light modulator control unit 621 and a light sourcecontrol unit 622. And it processes the input image signal data asdescribed for the single plate image display apparatus. The spatiallight modulator control unit 621, is basically similar to the onedescribed for the single plate image display apparatus. The SLM controlunit 621 is connected to the individual spatial light modulators 612,613 and 614. And it is capable of controlling the individual spatiallight modulators 612, 613 and 614 either independently or synchronouslybased on the image signal data processed by the processor. It is alsocapable of controlling the individual spatial light modulators 612, 613and 614 synchronously with other constituent members. The light sourcecontrol unit 622 is similar to the one described for the single plateimage display apparatus and is connected to the light source 601; and iscapable of controlling the light intensity of the light source, thenumber of sub-light sources to be turned on and such based on the imagesignal processed by the processor.

Frame memory 623 and an image signal input unit 624 are similar to theones described for the single plate image display apparatus andtherefore the description is omitted here. The above descriptionsprovide the specific details related to the constituent membersimplemented in the three-plate image display apparatus 600 shown in FIG.13.

The following description describes the principle of display of a colorimage at the three-plate image display apparatus 600 shown in FIG. 13.In the three-plate image display apparatus 600, the light emitted fromthe light source 601 is transmitted through condenser lens-1 602, rodintegrator 603, condenser lens-2 604, condenser lens-3 605 in sequenceand incident to the first prism 606 of the TIR prism 608 at a criticalangle or more. Then, the incident light is totally reflected by thefirst prism 606 of the TIR prism 608. The totally reflected light entersthe first dichroic prism 609. And only a light of the wavelengthequivalent to red, among the totally reflected light, is reflected,while the light of other wavelengths are passed, on the emission surfacefor light of the first dichroic prism 609 and/or on the incident surfacefor light of the second dichroic prism 610. Then, as for the lightentered the second dichroic prism 610, only a light of the wavelengthequivalent to blue, among the incident light, is reflected, while thelight of other wavelength, that is, a light equivalent to green, ispassed on emission surface for light of the second dichroic prism 610and/or incident surface for light of the third prism 611. The light,which enters the third prism, 611 and the third prism removes the lightof wavelengths equivalent to blue and red, while the green lightprojects along a straightforward direction in the third prism 611.

Then, the light selectively transmitted and reflected according to thewavelengths in each of these prisms are projected respectively to thepackages 615, 616 and 617 provided with the anti-reflection structure.The respective incident lights are projected onto the spatial lightmodulators 612, 613 and 614 that are placed on the respective sides ofthe first dichroic prism 609, second dichroic prism 610 and third prism611. The individual lights transmitted through the packages 615, 616 and617 enter the respective spatial light modulators 612, 613 and 614respectively provide with the anti-reflection structure as describedabove. The individual spatial light modulators 612, 613 and 614 aremutually independently controlled by the spatial light modulator controlunit 621 so as to respond to the respective lights based on the imagesignal processed by the processor 620. The individual spatial lightmodulators 612, 613 and 614 modulate and reflect the incident respectivelights. Then, the red light reflected by the spatial light modulator612, re-enters the first dichroic prism 609. Also, the blue lightreflected by the spatial light modulator 614, re-enters the seconddichroic prism 610. And the green light reflected by the spatial lightmodulator 613 re-enters the third prism 611. The red light re-enteringthe first dichroic prism 609, and the blue light re-entering the seconddichroic prism 610, and the red light and blue lights repeat thereflection processes when transmitting inside the respective prisms 609and 610. Then, the blue transmits in an optical path overlapped with theoptical path of the green light and re-entering the second dichroicprism 610 from the third prism 611, thereby the green light and bluelight are synthesized. Then, the synthesized light with the wavelengthsequivalent to green and blue enters the first dichroic prism 609 fromthe second dichroic prism 610. Then, the red light transmits on anoptical path overlapped with the optical path of the light equivalent tothe wavelengths of green and blue and entering the first dichroic prism609 from the second dichroic prism 610, thereby the red light issynthesized with the blue-green synthesized light inside the prism 610The synthesized light of the individual lights modulated by therespective spatial light modulators 612, 613 and 614 then enters thesecond prism 607 of the TIR prism 608 with an incident angle that issmaller than a angle. Then, the synthesized light is transmitted throughthe second prism 607 of the TIR prism 608 to project to the screen 619through a projection lens 618.

According to such optical transmissions, a color image is projected atthe three-plate image display apparatus.

With the three-plate configuration, when compared to the single-plateimage display apparatus described above, since each light of the primarycolors is displayed at all times, there will be no visual problem suchas the so-called color breakup. Furthermore, effective use of emittedlight from the light source provides in principle a bright image.

The present invention discloses embodiments provided with improvedfeatures to prevent an unnecessary reflection light occurred on aspatial light modulator and from the constituent members of a packagethat contains and protects the spatial light modulator in an imagedisplay apparatus. Improvements of display quality are achievedimprovement of the contrast of the displayed image.

The anti-reflection structure formed on the mirror and package surfaceseliminates a necessity of forming an anti-reflection layer. Furthermore,the anti-reflection structure possesses a low reflectivity in a widerange of wavelength band, providing a wide range of permissible incidentangles when configuring an optical system. Moreover, the antireflectivestructure provides a more effective and convenient design andmanufacturing method and configuration because there is no need toconsider a condition such as material selection, adhesiveness, thermalexpansion, diffusion, non-volatility and such when forming ananti-reflection layer.

Various alternations and modifications have no doubt become apparent tothose skilled in the art after reading the above disclosure.Accordingly, it is intended that the appended claims be interpreted ascovering all alternations and modifications as falling within the purespirit and scope of the invention.

1. An image projection system comprising: a spatial light modulator supported on a device substrate for controlling a light modulation element further including a hinge disposed on said device substrate to support a mirror at a distance above said device substrate to reflect and modulate an incident light emitted from a light source; an antireflection structure comprising cyclic protrusions extended from a surface of said device substrate underneath said light modulating element wherein a distance between two of said cyclic protrusions is shorter than a wavelength of an incident light for preventing a reflection of said incident light from said antireflection structure; said cyclic protrusions having a cross sectional shape of substantially side-by-side vertical triangles; and said side-by-side triangles is characterized by: λ>P>λ/2, and H/W>3, where the P is a pitch between top vertex points of the side-by-side triangles, the λ is the wavelength of the incident light, the H is the height of the side-by-side triangles, and the W is a base width of the side-by-side triangles.
 2. The image projection system according to claim 1 wherein: said antireflection structure is disposed on a backside of said mirror for preventing a reflection of light from said backside of said mirror.
 3. The image projection system according to claim 1 wherein: said antireflection structure is disposed on a top surface of said device substrate underneath a gap between two adjacent mirrors.
 4. The image projection system according to claim 1, comprising: the antireflection structure is disposed on a top surface of the device substrate adjacent to said hinge underneath said mirror.
 5. The image projection system according to claim 1, wherein: the spatial light modulator further comprising a plurality of light modulation elements each having a mirror for reflecting and modulating the incident light wherein said antireflection structure is disposed on a backside surface of the mirror of each of said light modulation elements.
 6. An image display apparatus comprising: a spatial light modulator modulating an incident light emitted from a light source; a device substrate for supporting said spatial light modulator thereon wherein said device substrate further includes an antireflection structure comprising cyclic protrusions extended from a top surface of said device substrate having a cross sectional shape of substantially side-by-side triangles wherein a distance; and said side-by-side triangles is characterized by: λ>P>λ/2, and H/W>3, where the P is a pitch between top vertex points of the side-by-side triangles, the λ is the wavelength of the incident light, the H is the height of the side-by-side triangles, and the W is a base width of the side-by-side triangles.
 7. The image projection system according to claim 6 wherein: said spatial light modulator is contained in a package and said antireflection structure is disposed on internal walls of said package for preventing a reflection from said internal walls of said package.
 8. The image projection system according to claim 6, wherein said spatial light modulator is contained in a package and said antireflection structure is disposed on outer walls of said package for preventing a reflection from said outer walls of said package.
 9. The image projection system according to claim 6, comprising: the cyclic structure is disposed on a top surface and a bottom surface opposite said top surface of the device substrate.
 10. The image display apparatus according to claim 6, further comprising a light source for projecting a polarized incident light, and the antireflection structure is oriented in one direction parallel with a polarization direction of the polarized incident light.
 11. The image display apparatus according to claim 6, further comprising a light source for projecting a polarized incident light, and the antireflection structure is oriented in one direction perpendicular to a polarization direction of the polarized incident light.
 12. The image projection system according to claim 6 wherein: said spatial light modulator is contained in a package with a cover member and said antireflection structure is disposed on a surface of said cover member.
 13. The image projection system according to claim 6 wherein: said spatial light modulator is contained in a package with a cover member and said antireflection structure is disposed on an inner surface and an outer surface of said cover member.
 14. A method of manufacturing a spatial light modulator for modulating an incident light projected thereon comprising applying an imprinting method, etching method or sol-gel method for forming an antireflection structure comprising a plurality of cyclic protrusions to having a cross sectional shape of substantially side-by-side triangles extend from a top surface of a device substrate preventing a reflection of said incident light from said antireflection structure; and said side-by-side triangles is characterized by: λ>P>λ/2, and H/W>3, where the P is a pitch between top vertex points of the side-by-side triangles, the λ is the wavelength of the incident light, the H is the height of the side-by-side triangles, and the W is a base width of the side-by-side triangles. 